7121/5-1

General

Wildcat well 7121/5-1 is located on the eastern part of the Snøhvit Field. It was drilled about 75 m down flank on the Alpha-structure in the block. The Snøhvit structure consists of an east-west running horst and a rotated normal faulted block. The main objective in the well was to test possible reservoir rocks of Jurassic/Triassic age as seen in neighbouring wells.

Operations and results

Well 7121/5-1 was spudded with the semi-submersible installation West Vanguard on 7 June 1985 and drilled to TD at 3200 m. The rig was shut down from 16 June to 30 June due to a strike. Otherwise drilling proceeded without significant problems. The well was drilled with spud mud down to 865 m, with a gypsum/polymer mud from 865 m to 1925 m, and with polymer mud from 1925 m to TD.

Top reservoir came in at 2369 m with hydrocarbons. From RFT pressure measurements the gas/oil contact was found at 2427.5 m and the oil/water contact at 2442 m. Logs displayed sands with possible hydrocarbons in Triassic sandstones, but increasing shale down hole reduced porosity/permeability and DST test confirmed a tight formation. Geochemical analyses showed immature rocks until 2250 m and marginal to significant maturity in Triassic/Jurassic rocks respectively. Nine cores were cut in the interval 2365 m to 2523 m in the Stø, Nordmela and Tubåen Formations. One core was cut from 3088 m to 3109 m in the Triassic Snadd Formation. Four RFT segregated samples were taken in the upper part of the Stø and Nordmela Formations from 2370 m to 2434 m, one in the Tubåen Formation at 2507 m, and one at 2802.7 m in the Snadd Formation. A small amount of condensate in the sample from 2370 m was the only reported liquid hydrocarbons from the RFT samples. Otherwise gas was recovered in the samples from 2424 m and 2370 m, while the sample from 2507 recovered mainly water/mud filtrate and minor gas. The sample from 2802.7 m contained only minor amounts of mud filtrate and no